Process for the oxidation of unsaturated alcohols

Abstract

The present invention relates to the field of organic synthesis and more precisely to a process for the synthesis of an unsaturated aldehyde or ketone by oxidation of the corresponding alcohol. The oxidation is performed by a hypochlorite salt and a catalytic amount of a N-(2,2,6,6-tetraalkyl-4-piperidinyl-N-oxyl)-2-amino-1,3,5-triazine compound, preferably a N-oxyl derivative of one of the polymers known under the trademark Chimassorb® 944 or 2020.

1. A process for the oxidation of an unsaturated alcohol of formula                  
 
       wherein:
 R 1  represents a hydrogen atom, a C 1  to C 20  linear, branched or cyclic saturated or unsaturated hydrocarbon group, said hydrocarbon group optionally being substituted and also optionally including one or two oxygen or nitrogen atoms; 
 R 2  represents a C 2  to C 20  linear, branched or cyclic alkenyl, alkandienyl or alkantrienyl hydrocarbon group, said hydrocarbon group optionally being substituted and also optionally including one or two oxygen or nitrogen atoms; or said R 1  and R 2  optionally may be bonded together to form an unsaturated ring having 5 to 20 carbon atoms, said ring optionally being substituted and also optionally including one or two oxygen or nitrogen atoms; wherein the optional substituents of R 1 , R 2  and of the ring which said R 1  and R 2  together may optionally form, are C 1  to C 15  linear, branched or cyclic alkyl, alkenyl or aromatic groups; 
 into a corresponding unsaturated aldehyde or ketone of formula                  
 
 
       wherein R 1  and R 2  are as defined in formula (I);
 wherein the oxidation is performed by a hypochlorite salt of formula
   M(OCl) n   (III) 
 
 
       in which M represents an alkaline metal, in which case n is 1, or an alkaline-earth metal in which case n is 2;
 and in the presence of a catalytic amount of a N-(2,2,6,6-tetraalkyl-4-piperidinyl-N-oxyl)-2-amino-1,3,5-triazine compound. 
 
     
     
       2. The process of  claim 1 , wherein the unsaturated alcohol is a compound of formula (I),                  
 
       wherein:
 R 1  represents a hydrogen atom; 
 R 2  represents a C 5  to C 15  linear, branched or cyclic alkenyl or alkandienyl hydrocarbon group, that is optionally substituted; or R 2  represents a C 7  to C 15  linear, branched or cyclic alkantrienyl hydrocarbon group that is optionally substituted; and 
 the optional substituents of R 2  are C 1  to C 8  linear, branched or cyclic alkyl, alkenyl or aromatic groups. 
 
     
     
       3. The process of  claim 1 , characterized in that the N-(2,2,6,6-tetraalkyl-4-piperidinyl-N-oxyl)-2-amino-1,3,5-triazine is of formula                  
 
       wherein z represents an integer from 1 to 20;
 R 3  represents, simultaneously or independently, a hydrogen atom or an oxyl radical (O.), with the proviso that at least one R 3  group is an oxyl radical; 
 X represents an oxygen atom or a —NR 4 -group; 
 R 4  represents, simultaneously or independently, a hydrogen atom, a 2,2,6,6-tetramethyl-4-piperidinyl group, a 2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl radical group or a C 1  to C 15  linear, branched or cyclic saturated or unsaturated hydrocarbon group, said hydrocarbon group optionally including one or two oxygen or nitrogen atoms; or two R 4  groups, bonded to the same nitrogen atom, may be bonded together to form a heterocycle having 5 to 7 members and which may contain an oxygen atom; 
 R 5  represents, simultaneously or independently, a hydrogen atom or a NR 6   2  group; 
 R 6  represents, simultaneously or independently, a hydrogen atom, a C 1  to C 20  linear, branched or cyclic saturated or unsaturated hydrocarbon group, a 2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl radical group, a 2,2,6,6-tetramethyl-4-piperidinyl group or a group of formula                  
 
 R 7  representing, simultaneously or independently, a hydrogen atom, a C 1  to C 12  linear or branched alkyl group, a 2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl radical group or a 2,2,6,6-tetramethyl-4-piperidinyl group; and 
 Y represents, simultaneously or independently, a C 2  to C 20  linear, branched or cyclic alkylene group optionally including one or two oxygen or nitrogen atoms. 
 
     
     
       4. The process of  claim 3 , wherein the N-(2,2,6,6-tetraalkyl-4-piperidinyl-N-oxyl)-2-amino-1,3,5-triazine compound is a polymeric or oligomeric compound of formula                  
 
       wherein z represents an integer from 2 to 10;
 m represents an integer from 2 to 12; 
 R 3  is as defined in  claim 3 ; 
 R 4  represents, simultaneously or independently, a hydrogen atom, a 2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl radical group, a 2,2,6,6-tetramethyl-4-piperidinyl group or a C 1  to C 10  linear or branched alkyl or alkenyl group; or two R 4  groups, bonded to the same nitrogen atom, may be bonded together to form a heterocycle having 6 members and which may contain an oxygen atom; and 
 R 8  represents, simultaneously or independently, a hydrogen atom, a C 1  to C 10  linear or branched alkyl or alkenyl group, a 2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl radical group, a 2,2,6,6-tetramethyl-4-piperidinyl group or a group of formula (V). 
 
     
     
       5. The process of  claim 4 , wherein the N-(2,2,6,6-tetraalkyl-4-piperidinyl-N-oxyl)-2-amino-1,3,5-triazine derivative is a N-oxyl derivative of the polymers having the CAS Registry Numbers 71878-19-8 or 192268-64-7. 
     
     
       6. The process of  claim 1 , wherein the hypochlorite salt is selected from the group consisting of NaOCl, KOCl and Ca(OCl) 2 . 
     
     
       7. The process of  claim 1 , wherein one of a bromide salt of formula M′Br or a bicarbonate of formula M′HCO 3  is added to the process, wherein M′ is an alkaline metal. 
     
     
       8. The process of  claim 1 , wherein a bromide salt of KBr or NaBr is added to the process. 
     
     
       9. The process of  claim 1 , wherein a bicarbonate of KHCO 3  or NaHCO 3  is added to the process. 
     
     
       10. The process of  claim 1 , wherein the catalyst has a concentration ranging from 0.02 to 0.15 molar equivalents relative to the amount of alcohol. 
     
     
       11. The process of  claim 1 , wherein the hypochlorite salt is added to the reaction mixture in an amount of between 0.9 and 2.5 molar equivalents relative to the amount of alcohol. 
     
     
       12. The process of  claim 1 , which is carried out at a temperature ranging between 0° C. and 60° C. 
     
     
       13. The process of  claim 1 , conducted in a solvent. 
     
     
       14. The process of  claim 1 , conducted in the absence of a solvent.